Doctor blade heads may have one, two or more doctor blades. With two or/more doctor blades, an ink reservoir can be defined between the blades. Some doctor blades are employed to seal against an ink roll to form the bottom of an ink reservoir, while other doctor blades are used for doctoring the thickness of the ink film on the ink roll, and such blades may be orientated as so called reverse angle doctor blades.
In printing, various configurations of doctor blade heads have been employed, including a head having two doctor blades with the ink reservoir contained therebetween, one doctor blade forming the bottom of the reservoir and the other being a reverse angle blade for doctoring the ink film.
Doctor blade heads are employed in flexographic printing apparatus and individual machine sections.
In Ward, Jr. et al U.S. Pat. No. 3,116,688, a doctor blade head is disclosed in which an inflatable air tube is employed to flex a doctor blade against an ink fountain roll. An air tube is disclosed in pending U.S. patent application Ser. No. 310,065 (subsequently granted as Harrison et al U.S. Pat. No. 5,003,876) to pivot a doctor blade head against an anilox roll.
An air tube has been found to provide good control over the pressure by which the blade or blades of a doctor blade head can be pressed against an ink roll.
It is also known to provide end sealing arrangements at the ends of any ink reservoir in a doctor blade head. Examples of such end sealing arrangements are disclosed in Ward, Jr. et al and Harrison et al referred to above.
However, with the desire for higher quality printing on containers, particularly corrugated paperboard container blanks printed by flexographic printing presses, the performance of existing doctor blade heads has become more critical.